Expanded particles of synthetic resins such as polystyrene, polyethylene and polypropylene are molded in various forms and widely used as packing medium, cushioning medium and insulation. After being used, expanded particle moldings are generally crushed with a crusher and then burnt up or buried under the ground. When the resins are burnt up, environmentally harmful gases such as carbon monoxide and carbon dioxide are generated in a large amount, and resins including chloride and nitrogen generate various types of gases poisonous to living things. Also, it is necessary to secure land to bury crushed resins under the ground. For the purpose of recycling the crushed resins, expanded particle moldings produced from the same resin must be collected. It requires a great deal of labor to select resins.
Japanese Patent Application Laid-Open Nos. 83145/1988 and 119687/1977 disclose a process for recovering recyclable resin chips from expanded particle moldings. The process comprises crushing expanded particle moldings comprising, for example, polystyrene or polyethylene, heat-melting the crushed expanded particle moldings to remove gas generated from the particles present in the melted resin, extruding the melted resin in a filament form and cutting the extruded resin into proper sizes. The recovered resin chips, however, have the drawbacks in that moldings of good quality cannot be produced therefrom because the resin chips have lost, in the recovering process, their suitable properties for expansion due to deterioration during heating and mixing of foreign substances therewith.
Japanese Patent Application Laid-Open No. 278939/1991 and German Offenlegungsshrift No. 2,462,040 disclose a process for mechanically separating expanded particles from expanded particle moldings of polystyrene or polyethylene and the like in a crusher. According to this process, expanded particle moldings are directly crushed by mechanical force. As a result, the recovered expanded particles tend to be mechanically damaged. Moreover, in this process, individual expanded particles are not completely separated so that there remain blocks of the expanded particles.
An object of the present invention is to solve the above problems and to provide a process for recovering recyclable expanded particles from used expanded particle moldings comprising synthetic resin, without producing bad effects on the environment.